Report for Shreadvector (and everyone else here)
 

Hello All,

Not long ago, Shreadvector had expressed curiosity about how stable the Estes UP Aerospace SpaceLoft rocket (see: http://www.estesrockets.com/rockets...space-spaceloft ) is, considering its general similarity to the Gnome (see: http://www.estesrockets.com/rockets...-bulk-pack-24pk ), a rocket which has had stability problems (especially with A10-3T motors) since the new finger tab-equipped motor clips replaced the original motor clips. In mini motor-powered rockets with BT-5 body tubes or BT-5 motor mount tubes, the finger tab extends inward close to the motor nozzle, and sometimes (especially with the A10-3T, whose nozzle is larger) the motor's exhaust plume strikes the finger tab, which acts as a jet vane and makes the rocket veer off course or even go unstable. This afternoon I had an opportunity to flight test an Estes UP Aerospace SpaceLoft, and I figured that Shreadvector (as well as many other YORF members) would find these flight results useful. Here is what happened:

I made two flights using 1/2A3-4T motors of recent manufacture and one flight using a 1/2A3-2T motor that was made in the early 1990s (both of these motors are on the rocket's recommended motors list). My UP Aerospace SpaceLoft is equipped with a modified recovery system, which had a marked effect on the flight results. It has a "non-stock" shock cord--9" of 100# Kevlar cord that is tied to 11" of 1/16" diameter round elastic cord (not counting the short "extra" lengths of both cords that are accounted for by knots). The provided streamer is attached to the shock cord via a 1/8" diameter hole punched near the edge of one end (the hole is reinforced with a ~1" X ~1" piece of clear plastic packing tape that was folded over the end of the streamer before the hole was punched), and the streamer is free to slide up and down the elastic portion of the shock cord, and the streamer was packed into the rocket adjacent to the nose cone base for all three flights. The launches were made from a Quest launch pad with a standard 36" launch rod, and they went as follows:

[FLIGHT #1 -- Motor: 1/2A3-4T] The SpaceLoft was launched into a light (~5 mph) wind and weather-cocked only slightly, curving over somewhat more during the last second of coasting. Stability was surprisingly positive, considering the model's small fins (the clay-ballasted nose cone and the long body tube were undoubtedly factors); the smoke trail showed a few small "kinks" as the rocket corrected itself in response to varying winds aloft. Ejection was very near apogee (estimated to be approximately 350 feet), with the rocket nearly stationary in the air. It fell with its body tube and shock cord horizontal, which prevented the motor clip's finger tab from striking the ground first. Touchdown was about 220 feet downrange, and the rocket suffered no damage.

[FLIGHT #2 -- Motor: 1/2A3-4T] This time the rocket was launched with the wind (which was again ~5 mph), which caused it to climb almost straight up. Only two or three small "kinks" were evident in its smoke trail. Ejection was again very close to apogee (estimated to be nearly 400 feet), with the rocket moving very slowly. As before, the rocket fell in a horizontal attitude, landing undamaged about 150 feet from the launch pad.

[FLIGHT #3 -- Motor: 1/2A3-2T] The casing of this older motor had swollen slightly, making it impossible to slide the motor all the way into the rocket. Approximately 1/2" of the rear end of the motor was left protruding from the rear end of the rocket, and a strip of masking tape was applied to both the motor and the fin unit to prevent the motor from kicking itself out at ejection. Despite its age and swollen casing, this 1/2A3-2T motor worked perfectly. The rocket was launched with the (~5 mph) wind again, rising nearly vertically, and the farther-protruding motor caused no stability problems. Ejection occurred at a considerably lower altitude than before (approximately 200 feet), with the rocket still climbing at a significant velocity. It fell in a horizontal attitude as before, landing about 90 feet from the launch pad. The shock cord and streamer were not damaged, but the front edge of the rocket's body tube had a large dent; no doubt this happened because the rocket was still moving at a good clip at ejection, causing the heavy nose cone to snap back. So, in summary:

Based on this admittedly very small statistical sample, it would appear that the 1/2A3-4T is a nearly-ideal motor for the UP Aerospace SpaceLoft, while the 1/2A3-2T does not provide sufficient coasting time for the rocket to slow down to a safe velocity for recovery system deployment. (A Gnome that I also flew this afternoon flew high--and stably--and ejected its streamer approximately at apogee on 1/2A3-4T motors.) The full A3-4T (another motor on the SpaceLoft's recommended motors list) may work fine in the rocket, but I would be leery of trying the (also-recommended) A10-3T in this model for two reasons: [1] Its larger nozzle (and thus wider exhaust plume) increases the risk of causing the "motor clip finger tab jet vane effect," and [2] this motor's high burnout velocity combined with its short (3-second) delay might result in relatively high-velocity recovery system deployments, which could lead to broken or damaged shock cords, separated or damaged streamers, and/or dented body tubes.

I hope this information will be helpful.

Estes now seems to recommend whatever motors "fit" regardless of flight pattern or delay time. I do not recall that being the case in the distant past. Perhaps that is something that needs fixin'.

I always preferred the longer delay mini motors for almost all rockets. It seemed to me virtually only the Gooneybirds needed short delays.

Jerry

I normally cut off the finger tab on the mini motor hooks to avoid the problem that you mentioned about the exhaust hitting the finger tab. All you need to fix these hooks is a set of needle nose pliers, a vise, and a Dremel tool with a cut off wheel. Semroc and Apogee sell the older style (1992 and earlier) EH-3s without the finger tab.

Or eliminate it to save trouble and mass at the same time and retain motors with tried and true tape.

Indeed--and they also sometimes leave perfectly "good-fitting" (in terms of total impulse and delay time versus drag) motors off kits' recommended motors lists. For example, the 1/2A3-4T is not included in the Bandito's recommended motors list, but it flies very well (and ejects the 'chute at or near apogee) when flown on that motor.Yes, those look like they would need the 1/2A3-2T. Likewise for heavier mini motor rockets like the all-plastic Firestreak SST.I agree, but since kids who would be flying SpaceLoft or Gnome rockets at Fred's Club's launches would be novices who would almost certainly build their kits "stock," I wanted to test the "worst case" (for stability) scenario that involves the finger tab.That's how *my* SpaceLoft rockets are built (the one that I test-flew yesterday had come with one end of its body tube mashed and creased, so I glued the fin unit onto that end and installed the motor clip to make it the test rocket).

I like the finger tabs. As time goes by, my fingers aren't as agile as they used to be...
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I never found the original mini engine hooks easy to use, so I must agree. I just wish Estes would modify them so that the finger tabs would clear the nozzles of A10-3T motors and avoid the "jet vane affect."

If Estes used a bend similar to the bend used by Quest and Custom, the finger tabs would not be such a problem. YMMV.

I concur. While I haven't yet seen a Custom kit "in person," I have cut Quest motor clips down to mini motor length and bent new forward "tangs" in them to restrain the motors from moving forward in the rockets. The Quest motor clips' finger tabs cleared the mini motors' nozzles while providing positive motor retention in the rearward direction.

The Quest and Custom motor hooks appear to be identical. However, they do not retain reloadable motors worth a darn. Ask me how I know. :( :eek: